1. Field of the Invention
The invention relates to a fluid catalytic cracking process. More particularly the invention relates to the regeneration of coked fluid catalytic cracking catalyst. Most particularly the invention relates to steam decoking of catalyst to yield a hydrogen-rich gas.
2. Other Related Methods in the Field
The fluid catalytic cracking (FCC) process is well-known. State of the art commercial catalytic cracking catalysts for this process are highly active and selective for converting hydrocarbon charge stocks to liquid fuel products. With such active catalysts it is preferable to conduct catalytic cracking reactions in a dilute phase transport type reaction system with a relatively short period of contact between the catalyst and the hydrocarbon feedstock.
In a state of the art process, a regenerated catalyst is fluidized in the lower portion of a riser transport line reactor and mixed with a hydrocarbon charge stock. Hydrocarbon conversion products including a liquid fuel boiling range product, gas and coked catalyst are discharged from the upper end of the riser reactor into a reactor vessel. In the reactor vessel, coked catalyst is separated in a cyclone separator and passed to a stripping section where hydrocarbon vapors are steam stripped from the catalyst. The resulting coke contaminated catalyst, termed spent catalyst, is collected in a spent catalyst standpipe and passed to a vertically arranged regenerator vessel containing a fluidized dense phase catalyst bed. The fluidization is maintained by upwardly flowing oxygen containing regeneration gas introduced by a gas distributor into the lower portion of the dense phase catalyst bed contained in the bottom of the regenerator vessel. Regeneration gas is supplied in excess of that required for complete oxidation of coke as indicated by the analysis of oxygen in flue gas. Above the dense phase catalyst bed is a dilute phase bed wherein residual carbon is oxidized at a temperature higher than in the dense phase bed. Reactivated catalyst, substantially reduced in coke (0.15 wt % or less) is passed vertically upwardly by the fluidizing regeneration gas to an upper portion of the dilute phase bed and into a regenerated catalyst standpipe where it is collected for reuse in the riser reactor.
U.S. Pat. No. 4,481,103 to F. J. Krambeck et al. discloses a fluid catalytic cracking (FCC) process for converting a sulfur containing hydrocarbon charge. Spent catalyst is subjected to steam stripping at a temperature of 500.degree. C. to 700.degree. C. for 1 to 10 minutes in the absence of oxygen. As a result, coke and sulfur are removed from the catalyst.